In the field of aircraft manufacture, electrical wiring extends to all parts of the aircraft from the cockpit, and many cables and individual electrical conductors are passed through bulkheads between the aircraft's fuselage and its wings or its tail, the cables and/or conductors being grouped together and passed through orifices formed at selected positions in the bulkheads. In use, the fuselage of an aircraft is commonly pressurized whereas the wings and tail are not, and, in order to maintain this pressure differential, it is necessary to provide appropriate pressure sealing of the orifices.
Conventional cable sealing glands for use in ships and in buildings make use of packing pieces to seal the passage of a relatively small number of cables having a limited range of sizes through bulkheads and the like. However, in an aircraft, and particularly a technologically sophisticated computer controlled "fly by wire" aircraft, the number of cables and electrical conductors that have to be passed through bulkheads is legion, and there are considerable size differences between the thinnest of single-core conductors, which have sub-millimeter diameters, and larger multiple-conductor cables. The use of packing pieces in aircraft applications is thus impractical and the most commonly used sealing method makes use of an elastomeric bung through which the respective cable/conductor bundle is threaded. The bung is then forced into a receptacle fitted in the bulkhead and is sealed therein by the liberal application of a silicone rubber sealing compound which is intended to wick into the interstices between the bundled cables/conductors so as to provide an effective pressure seal. However, in practice, this type of pressure seal tends to leak, as not all the gaps in the seal are reliably filled by the sealing compound. This problem is accentuated by high-pressure differentials across the seal and by cyclical pressurization and depressurization in normal use.
Another problem with the conventionally used arrangement is that it relies on a sufficient bundle of cables/conductors being passed through the elastomeric bung in order to produce optimum results. When it is desired to pass only a few small cables through a particular bulkhead orifice, the hole through the bung can be too large in comparison to the size of the cable bundle for the sealant, which is quite fluid, to form an effective seal.